OPPORTUNITIES AND CHALLENGES: 40AR/39AR K-FELDSPAR THERMOCHRONOLOGY
Advancing the future of the MDD method appears to lay in fully utilizing microbeam sample characterization coupled to high precision argon analysis on the same characterized K-feldspar fragment or spot. Recent increases in precision and sensitivity provided by new multi-collector mass spectrometers reveal new challenges towards understanding the details of the MDD method, but more importantly open new levels of opportunity. MDD analysis of tiny fragments of multiple generations of alkali-feldspars from within single rocks is the path forward towards fully exploiting the information embodied within in the argon isotopic system. Extracting both thermal and fluid histories are the challenges and the opportunities that are within reach because of new technologies. Examples of combined microbeam chemistry and argon extraction that provide new insight and also reveal complexities are provided by detailed work on the Klokken syenite, Chain of Ponds pluton and Shap granite. Incompatibilities of thermal histories from individual K-spar fragments are generally found to be caused by low temperature growth of 2nd generation K-spar. Dating this generation provides new opportunities for understanding rock histories. Avoiding this generation when selecting material for MDD analysis minimizes method complexity and improves thermal history accuracy.